1. Field of the Invention
The field of this invention relates to a method for providing stable coal-oil mixture fuel slurries and novel stable coal-oil mixture fuel slurries.
2. Prior Art
With the rising cost of petroleum, coal has attracted renewed interest as a fuel. One potential way of using coal as a fuel is to form mixtures of coal and oil. Coal-oil mixtures can have the following advantages over coal particles alone.
(1) Coal-oil mixtures are higher in the calorific value than coal. PA0 (2) With some modification, existing petroleum combustion equipment can be used. PA0 (3) Marine transportation by tankers is possible such that large quantities of coal can be transported at high efficiency. PA0 (4) Long-distance land transportation (pipe line transportation) is possible. PA0 (5) Spontaneous combustion of coal during transportation can be prevented and therefore, it becomes possible to export brown coal which has not been exported in spite of its low price because spontaneous combustion readily occurs in brown coal. PA0 (6) Storage space at the site of use can be reduced. PA0 (1) contacting an aqueous slurry of coal particles containing ash and iron pyrite mineral matter with a promoting amount of at least one conditioning agent capable of modifying or altering the existing surface characteristics of non-pyritic ash and the pyrite under conditions to effectuate alteration or modification of at least a portion of non-pyritic ash and the contained pyritic sulfur; PA0 (2) agglomerating the coal particles while said ash and pyrite surfaces are altered or modified in PA0 (3) separating coal hydrocarbon oil agglomerates from at least a portion of the iron pyrite mineral matter and ash; and PA0 (4) mixing the separated coal hydrocarbon oil agglomerates with a quantity of fuel oil to form a coal-oil mixture of enhanced stability. PA0 (1) contacting an aqueous slurry of coal particles containing ash and iron pyrite mineral matter with a promoting amount of at least one conditioning agent capable of modifying or altering the existing surface characteristics of the pyrite under conditions to effectuate alteration or modification of at least a portion of ash and the contained pyritic sulfur; PA0 (2) agglomerating the coal particles while said pyrite surfaces are altered or modified in an aqueous medium with hydrocarbon oil; PA0 (3) separating coal hydrocarbon oil agglomerates from at least a portion of the iron pyrite mineral matter and ash; and PA0 (4) mixing the separated coal hydrocarbon oil agglomerates with a quantity of fuel oil to form a coal-oil mixture of enhanced stability.
A known problem of coal-oil mixtures is that the mixtures are not stable, i.e., denser coal particles tend to separate or settle from the less dense fuel oil. Heretofore, attempts have been made to stabilize mixtures of coal and oil to prevent the mixture from separating into its components.
For example, British Pat. No. 1,523,193 discloses more stable mixtures of coal and fuel oil are obtained by employing coal particles having a particle size below 10 microns. While employing coal particles haveing a particle size below 10 microns may increase stability, reducing coal particles to this size can be difficult and expensive.
U.S. Pat. No. 4,171,957 to Moriyama discloses adding various sulfonated compounds to mixtures of coal and fuel oil to stabilize the mixture. U.S. Pat. No. 4,201,552 to Rowell et al discloses various quaternary ammonium salts can stabilize coal-oil mixtures. These stabilizing compounds are not wholly satisfactory for stabilizing coal-oil mixtures because they introduce undesirable sulfur and nitrogen compounds to the fuel which can form pollutants on burning.
In short, while much attention has been directed heretofore for forming stable mixtures of coal and fuel oil, there remains an existing need for identifying more suitable ways for forming stable mixtures of coal and fuel oil for use as fuels.